1. Field of the Invention
The present invention relates to a solid electrolytic capacitor and a method for preparing the same; and more particularly to, a solid electrolytic capacitor which can be prepared without an additional lead frame by forming a cathode lead layer at one side of a capacitor element coupled with an anode wire with a conductive paste and forming an anode and a cathode at both sides of the capacitor element by a coating layer being in contact with the wire and the cathode lead layer, and a method for preparing the same.
2. Description of the Related Art
In general, a solid electrolytic capacitor is one of electronic components used for the purpose of cutting off a D.C. current and passing an AC current in addition to storing electricity and a tantalum capacitor is representatively prepared as the solid electrolytic capacitor.
The tantalum capacitor is used for general industrial equipment and in an application circuit having a low rated voltage range, and particularly, it is primarily used to reduce noise of a circuit or a portable communication apparatus having a defective frequency characteristic.
Such capacitor is prepared by inserting a lead wire into a center portion of a tantalum element or a portion excluding the center portion, or bending the inserted lead wire in an outside of the tantalum element.
A method of leading an anode terminal through spot-welding an anode lead wire and an anode lead frame to each other, and a method of leading an electrode terminal by anode and cathode lead forming after mold packaging are used as a method of assembling the lead frame to the tantalum element.
FIGS. 1 and 2 show a conventional solid electrolytic capacitor. FIG. 1 is a perspective view of the conventional solid electrolytic capacitor and FIG. 2 is a cross-sectional view of the conventional solid electrolytic capacitor.
As shown in the figures, a conventional solid electrolytic capacitor 10 includes a capacitor element 11 made of a dielectric powder material for determining a capacitance and a characteristic of a capacitor, anode and cathode lead frames 13 and 14 connected to the capacitor element 11 so as to easily mount the solid electrolytic capacitor 10 on a printed circuit board (PCB), and an epoxy case 15 molded with an epoxy to protect the capacitor element 11 from an external environment and make a shape of the capacitor element.
At this time, the capacitor element 11 has a rod-shaped anode wire 12 protruding from a portion thereof by a predetermined length.
The anode wire 12 is provided with a press surface 12a having a flat outer surface in order to increase a contact ratio with the anode lead frame 13 and prevent horizontal swing in welding.
Herein, the capacitor element 11 is prepared by forming dielectric powder in a rectangular parallelepiped shape and sintering it in a press process, forming a dielectric oxide coating film on an outer surface of the capacitor element 11 in a transformation process, and forming a manganese dioxide layer made of a solid electrolyte on the outer surface through pyrolysis by immersing the dielectric oxide coating film in a manganese nitrate solution.
A process of connecting the anode and cathode lead frames 13 and 14 to the capacitor element 11 prepared in the above-described manner includes the steps of leading the anode terminal by welding the plate-shaped anode lead frame 13 to the press surface 12a of the rod-shaped anode wire 12 protruding on the one portion of the capacitor element 11 by the predetermined length and leading the cathode terminal with a conductive adhesive applied to an outer surface of the capacitor element 11 or the cathode lead frame 14.
The preparation of the capacitor is completed through a marking process after forming the epoxy case 15 by molding the capacitor element 11 electrically connected to each of the anode and cathode lead frames 13 and 14 with the epoxy.
The conventional solid electrolytic capacitor 10 prepared in the above-described manner has a problem that a capacitance decreases and an impedance increases as the volumetric efficiency of the capacitor element 11 is remarkably lowered in an entire volume including a volume of the epoxy case 15.
In the conventional solid electrolytic capacitor 10, high-temperature heat is generated in the course of welding the anode wire 12 and the anode lead frame 13 directly to each other. AT this time, the generated heat has an influence on the capacitor element 11 through the anode wire 12, thereby damaging the capacitor element 11 vulnerable to heat.
Accordingly, a dielectric substance is broken by a heat shock, resulting in deteriorating a characteristic of a product and causing a failure, thereby increasing preparation cost.